1. Field of the Invention
The present invention relates to overhead airbag inflation systems in motor vehicles. More specifically, the invention relates to a compressible airbag module design for overhead airbag applications.
2. Description of Related Art
Inflatable airbags are well accepted for use in motor vehicles and have been credited with preventing numerous deaths and injuries. Some statistics estimate that frontal airbags reduce the fatalities in head-on collisions by 25% among drivers using seat belts and by more than 30% among unbelted drivers. Statistics further suggest that with a combination of seat belt and airbag, serious chest injuries in frontal collisions can be reduced by 65% and serious head injuries by up to 75%. Airbag use presents clear benefits and vehicle owners are frequently willing to pay the added expense for airbags.
The inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles. Airbags are typically installed in the steering wheel and in the instrument panel on the passenger side of a car. In the event of an accident, an electronic control unit (ECU) within the vehicle measures the abnormal deceleration via an accelerometer and triggers the ignition of an explosive charge. Expanding gases from the charge fill the airbags, which immediately inflate in front of the driver and passenger to protect them from impact against the windshield or instrument panel.
An airbag cover, also called a trim cover panel, covers a compartment containing the airbag module and may reside on a steering wheel, dashboard, vehicle door, along a vehicle roof rail, vehicle wall, or beneath the dash board. The airbag cover is typically made of a rigid plastic and may be forced open by the pressure from the deploying airbag. In deploying the airbag, it is preferable to retain the airbag cover to prevent the airbag cover from flying loose in the passenger compartment. If the airbag cover freely moves into the passenger compartment, it may injure a passenger.
Airbag apparatuses have been primarily designed for deployment in front of the torso of an occupant between the upper torso of an occupant and the instrument panel. Conventional airbags, such as driver""s or passenger airbags (hereinafter referenced as the xe2x80x9ctraditional airbagxe2x80x9d), protect the occupant""s upper torso and head from colliding with a windshield or instrument panel. Traditional airbag modules for frontal occupant protection deploy from the instrument panel (passenger side) or from the steering wheel (driver side). This location has several disadvantages including poor out of position (OOP) performance and unaesthetic visible instrument panel or steering wheel tear seams.
In fact, many known airbags have poor OOP performance for occupants. These airbags tend to direct the initial deployment energy toward the expected position of the occupant. While these designs help a properly positioned occupant avoid injury, placement of the airbag too close to an OOP occupant increases the risk that the occupant will be injured by the airbag itself. The speed at which the airbags in general, and especially front impact airbags, must deploy to adequately protect people requires that they inflate with considerable speed and force. With an OOP occupant, the risk of injury dramatically increases, as the models used to calculate desired deployment are considerably different. For example, an OOP occupant is most likely not wearing a safety restraint, whereas, the expected occupant position calculations generally anticipate that the occupant is wearing a seatbelt. Without a seatbelt, the inertia of the OOP occupant keeps them moving forward towards the instrument panel and windshield. The inertial motion of the OOP occupant also amplifies the force of the impact of the OOP occupant with the airbag over a properly restrained occupant. Furthermore, because the OOP occupant may be closer to the windshield and instrument panel, the airbag has less time to be successfully deployed. This dramatically increases the likelihood that the OOP occupant will have a secondary impact with the vehicle as the airbag does not have time to be properly deployed. Accordingly, a need exists for an airbag module that also provides protection to an OOP occupant.
In addition to poor OOP performance, airbags of all types known in the art have a number of additional disadvantages. One exemplary disadvantage of traditional airbag configurations is that they are too bulky for convenient overhead installation and use within a vehicle. Some vehicles simply do not have the vertical space in the roof of the vehicle to accommodate the bulk of certain cushion members and their respective inflators, such as those necessary for traditional overhead airbag configurations. Some attempt to build an overhead compartment, but as previously discussed, the traditional cushion member of an airbag, which is the portion impacted by a vehicle occupant, must be mounted some distance from a passenger, because the airbag requires space to inflate. This distance constraint further limits the available overhead locations for installation of frontal airbag systems. Accordingly, a need also exists for a thin overhead airbag module.
Yet another disadvantage is that previously known airbags are somewhat expensive to produce and install. For example, each airbag is typically a single-use device that includes an inflation device, a monitoring device, an inflatable airbag cushion and a support structure. These individual components are typically specialized for use in the airbag and are thus relatively more expensive than off the shelf components. Furthermore deployment of the airbag typically ends the usefulness of the unit and if the vehicle is still useable, requires airbag replacement. Additionally, deployment often requires the airbag to break through tear seams in the steering wheel or instrument panel. Thus, replacement of the airbag also requires replacing the damaged instrument panel or steering wheel cover further increasing the installation cost. Accordingly, a need exists for an airbag module with reduced replacement costs.
The typical deployment mechanisms used in available airbags create other disadvantages. For example during normal operation, the monitoring device of the airbag will detect irregular acceleration or deceleration and activate the inflation device. The inflation device is typically either a pyrotechnic or gas inflator that quickly introduces filler material, such as expanding gases, into the airbag cushion. The need for fast inflation rates can increase the risk that the filler material is introduced into the airbag too fast, causing the airbag to over inflate and break. Traditionally, inflation via the introduction of filler materials pushes the inflatable airbag cushion out of the airbag support structure. Unfortunately, an inflation process that pushes the inflatable airbag out of the support structure can also damage the inflatable airbag cushion if the cushion gets caught against the support structure or another sharp edge. Occasionally, the inflatable airbag cushion is improperly packaged within the support structure or is punctured as it pushes through the support structure during deployment. The result in either case is an improper or unsuccessful deployment of the airbag, which may result in injury to the occupant. What is needed is a deployment mechanism that avoids pushing the inflatable airbag cushion out of the support structure.
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available airbags. Thus, it is an overall objective of the present invention to provide a thin overhead airbag solution.
To achieve the foregoing objective, and in accordance with the invention as embodied and broadly described herein in the preferred embodiment, a thin overhead airbag apparatus configured to protect occupants of a vehicle from impact is provided. The thin overhead airbag apparatus includes a compressible housing assembly, an inflatable airbag cushion, and an inflator. The housing assembly holds the airbag cushion prior to deployment and more importantly is configured to be installed in the roof space of a vehicle. Typically this space is less than 40 mm thick, which would limit the size of airbag that could be used in conjunction with the apparatus. Fortunately, the housing assembly is compressible allowing a larger airbag cushion to be packaged within the apparatus. The stepped geometry of the compressible housing assembly allows for post-assembly compression without pinching the cushion that is packaged within. In one configuration, compression reduces the available packaging volume within the housing assembly by at least 20%. Compression may also provide the housing assembly with integrated rivets that are created during compression. Prior to compression the housing assembly may consist of an upper housing and a deformable lower housing. The inflatable airbag cushion is attached along the leading longitudinal edge to the compressible housing assembly. The inflator is in fluid communication with the cushion, the inflator providing an inflation force upon impact.
According to one configuration, the thin overhead airbag apparatus may further include an inflatable airbag cushion that is pulled from the housing during deployment. During deployment, the thin overhead airbag apparatus first inflates the cushion substantially parallel to the windshield. The cushion, which descends from the header or frame member of the vehicle to cover a majority of the area between the occupant and the front of the vehicle interior, first appears much like a curtain covering the front vehicle window or windshield. The first inflated section of the airbag cushion pulls the non-inflated portion of the cushion from the housing assembly. Once the inflatable airbag cushion has been completely pulled from the housing, the cushion begins expanding towards the expected occupant position. This inflation process provides better OOP protection by protecting the occupant from impact with the front window, flying shards of glass, and other projectiles. The overhead airbag may also help to keep the OOP occupant inside the vehicle during an endover or hard stop/frontal collision rollover accident. The secondary inflation expands towards the expected occupant position. As such, the thin airbag apparatus further protects an OOP occupant, because the secondary inflation pushes the OOP occupant back to the position where most safety constraints are directed.
Alternatively, the compressible housing may also include a deformable guide structure. This guide structure provides a deployment opening for the airbag cushion. The guide structure directs the initial inflation of the airbag cushion, so that the cushion inflates in a manner substantially parallel to the windshield. One configuration allows the guide structure to become deformed during deployment. The deformed guide structure becomes wider so that the cushion can be quickly pulled from the housing assembly.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.